Nineteenth century geologists recognized that rocks formed slowly as mountains eroded and sediments settled on the ocean floor.
But they could not say just how long such processes had taken, and thus how old their fossils were.
And by comparing the ratios of those atoms to atoms from meteorites, they could estimate how long ago it was that the Earth formed along with the rest of the solar system.
In 1956 the American geologist Clair Patterson (left) announced that the Earth was 4.5 billion years old.
The sun was once thought to burn like a coal fire, but physicists showed that it actually generates energy by slamming atoms together and creating new elements.
Then followed years of study and debate involving him and other investigators and politicians over control of lead in the environment.
In the end, his basic views prevailed, resulting in drastic reductions in the amount of lead entering the environment.
Tilton Clair Patterson was an energetic, innovative, determined scientist whose pioneering work stretched across an unusual number of sub-disciplines, including archeology, meteorology, oceanography, and environmental science—besides chemistry and geology.
He is best known for his determination of the age of the Earth.